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To reduce the end-to-end delay in EH-WSNs (energy-harvesting wireless sensor networks), medium access control protocols using pipelined-forwarding have been introduced and studied. In real-life applications, there are several situations where it is difficult to harvest more energy than the energy consumed. Therefore, it is crucial to design a MAC protocol that allows nodes to efficiently relay data without exhausting the power in pipelined-forwarding multihop transmission. In this paper, we propose a PP-MAC (priority-based pipelined-forwarding MAC) protocol that determines the priority of relay nodes based on the residual power and energy-harvesting rate. The proposed protocol determines the probability of a node becoming a relay node based on the priority of the node and attempts to access the channel in a distributed manner. Furthermore, the PP-MAC protocol controls the sleep interval based on the power conditions of the nodes. It also minimizes the power exhaustion problem by controlling the sleep interval based on the priority of the nodes. The performance of the proposed PP-MAC was evaluated via computer simulation, and the results indicated that PP-MAC could improve the network lifetime by mitigating the power imbalance of nodes.

It is important that using of efficient radio resource because of deficiency spectrum problem, so that related to this problem many researches are have proceeded. To solve this problem, Cognitive Radio(CR) was suggested. The channels are allocated to the secondary users when the primary users don`t use the channels, and unfairness of secondary users can be serious problem and channel quality of multichannel can be different due to the different traffic pattern of primary users. In this paper, we propose MAC prtocol both of the user`s fairness and channel quality in CR networks. Simulation results show the comparison with CR MAC protocols.

Spectrum handoff is the process of exchanging progressing data transmission from the current channel to another idle channel. The essential goal of spectrum handoff in CR(Cognitive Radio) networks is to perform consistent data transmission while sustaining performance of ongoing transmission of secondary users. This handoff procedure can cause additional latency that eventually affects on the performance of CR transmission. Channel prediction method is expected to avoid the disruption to primary users and to reduce the handoff latency. In this paper, adaptive channel prediction is proposed to cope with time-varying channel and an adaptive channel prediction based proactive handoff procedure is designed to enhance data transmission performance.

Cognitive radio (CR) has been proposed to solve the spectrum utilization problem by dynamically exploiting the unused spectrum. In CR networks, a spectrum selection scheme is an important process to efficiently exploit the spectrum holes, and an efficient channel allocation scheme must be designed to minimize interference to the primary network as well as to achieve better spectrum utilization. In this paper, we propose a multichannel selection algorithm that uses spectrum hole prediction to limit the interference to the primary network and to exploit channel characteristics in order to enhance channel utilization. The proposed scheme considers both the interference length and the channel capacity to limit the interference to primary users and to enhance system performance. By using the proposed scheme, channel utilization is improved whereas the system limits the collision rate of the CR packets.

Cognitive radio technology enables us to utilize the extra spectrum which is not used by the primary users by sensing the channel condition. To use such an extra spectrum, spectrum allocation is one of the important issues in the cognitive radio networks. The network is dynamic and the available channels are changeable, and the opportunistic channel allocation is required to use the resource efficiently without interference to the primary networks. In this paper, modified proportional fairness scheduling is proposed for cognitive radio networks to satisfy the both fairness and system throughput, and the modified scheduling was designed to reduce the interference to the primary users.

Channel allocation is one of the important issues in the multichannel transmission. In the cognitive radio networks, channel allocation scheme should be designed to improve spectrum efficiency without interfering with the transmission of licensed users. In this paper, we propose a spectrum hole prediction based channel allocation scheme. The proposed channel allocation scheme, predicts spectrum hole by using the channel success rate, and limit the transmission of secondary user`s data, and it reduces the interference to the primary user. The performance of proposed channel allocation scheme is evaluated by the computer simulation.

— Opportunistic spectrum access (OSA) allows unlicensed users to share licensed spectrum in space and time with no or little interference to primary users, with bring new research challenges in MAC design. We propose a cognitive MAC protocol using statistical channel information and selecting appropriate idle channel for transmission. The protocol based on the CSMA/CA, exploits statistics of spectrum usage for decision making on channel access. Idle channel availability, spectrum hole sufficiency and available channel condition will be included in algorithm statistical information. The model include the control channel and data channel, the transmitter negotiates with receiver on transmission parameters through control channel, statistical decision results (successful rate of transmission) from exchanged transmission parameters of control channel should pass the threshold and decide the data transmission with spectrum hole on data channel. The proposed protocol’s simulation will show that proposed protocol does improve the throughput performance via traditional opportunistic spectrum access MAC protocol.

opportunistic spectrum access (OSA) allows unlicensed users to share licensed spectrum in space and time with no or little interference to primary users, with bring new research challenges in MAC design. We propose a cognitive MAC protocol using statistical channel information and selecting appropriate idle channel for transmission. The protocol based on the CSMA/CA, exploits statistics of spectrum usage for decision making on channel access. Idle channel availability, spectrum hole sufficiency and available channel condition will be included in algorithm statistical information. The model include the control channel and data channel, the transmitter negotiates with receiver on transmission parameters through control channel, statistical decision results (successful rate of transmission) from exchanged transmission parameters of control channel should pass the threshold and decide the data transmission with spectrum hole on data channel. A dynamical sensing range as a important parameter introduced to maintain the our protocol performance. The proposed protocol"s simulation will show that proposed protocol does improve the throughput performance via traditional opportunistic spectrum access MAC protocol.

One of the principal disadvantages of multicarrier modulation technique is the sensitivity to the frequency offset introduced by Doppler shift. This frequency offset introduces inter-carrier interference (ICI) among the multiplicity of carriers in the multicarrier modulated signal. However, Doppler spread induced by temporal channel variations can provides another means for diversity. In this paper, we propose a modified multicarrier code division multiple access (CDMA) system to exploit Doppler diversity as well as multipath diversity. The key work of our framework is a canonical time-frequency-based decomposition of the mobile wireless channel into series of independent fading channel. The decomposition naturally leads to a time-frequency generalization of the Rake receiver that exploits both multipath and Doppler diversity.

Cognitive radio (CR) has been recently proposed to dynamically access unused-spectrum. Since the spectrum availability for opportunistic access is determined by spectrum sensing, sensing control is identified as one of the most crucial issues of cognitive radio networks. Out-of-band sensing to find an available channels to sense. Sensing is also required in case of spectrum hand-off. Sensing process needs to be done very fast in order to enhance the quality of service (QoS) of the CR nodes, and transmission not to be cut for longer time. During the sensing, the PU(primary user) detection probability condition should be satisfied. We adopt a channel prediction method to find target channels. Proposed prediction method combines chaotic global method and chaotic local method for channel idle probability prediction. Global method focus on channel history information length and order number of prediction model. Local method focus on local prediction trend. Through making simulation, Proposed method can find an available channel with very high probability, total sensing time is minimized, detection probability of PU`s are satisfied.

In Cognitive Radio network, spectrum selection scheme is one of a important part to manage idle spectrums efficiently. However, in CR networks, they have to adopt time-varying channel availability to minimize the interference to primary users (PU), and be able to manage spectrum resources efficiently. In this paper, we proposed a modified PF scheduler which can be appropriate to schedule downlink CR users and channels, by considering the fairness and the throughput as well as the primary user characteristics of each channel.

Cognitive radio has been recently proposed to dynamically access unused-spectrum. Since the spectrum availability for opportunistic access is determined by spectrum sensing, sensing is identified as one of the most crucial issues of cognitive radio networks. The PHY-layer sensing, as a part of spectrum sensing in cognitive radio, concerns the sensing mechanism to determine channel to be sensed and to access. One of the important issues in the PHY-layer sensing control is to find an available sensing period and trade-off between spectrum sensing and data transmission. In this paper, we show the relationship between spectrum sensing and data transmission according to the sensing period. We analyze and propose the new scheme to evaluate optimal sensing period.

In a CR (cognitive radio) network, channel selection is one of the important issues for the efficient channel utilization. When the CR user exploits the spectrum of primary network, the interference to the primary network should be minimized. In this paper, we propose a spectrum hole prediction based channel selection scheme to minimize the interference to the primary network. To predict spectrum hole, statistic properties of primary user`s traffic is used. By using the predicted spectrum hole, channel is selected and it can reduce the possibility of interference to the primary user and increase the efficiency of spectrum utilization. The performance of proposed channel selection scheme is evaluated by the computer simulation.

Channel sensing in the cognitive radio networks is a very important function to avoid collision with primary users. MAC-layer sensing determines key parameters for channel sensing such as available sensing period and sensing duration. The sensing period and sensing duration affect on the data transmission. The shorter sensing period increases the sensing accuracy and reduces the possibility of packet collision with primary users. However, it can reduce the data transmission time and decrease the system throughput. Therefore, one of the important roles of MAC-layer sensing is to determine the sensing period. In this paper, we evaluate the sensing period to minimize the missing probability and interference probability to the primary users.

To minimize interference in the primary network is the most important requirement in CR (Cognitive Radio) networks. Channel allocation algorithm should be designed to improve spectrum efficiency without interfering in the transmission of licensed users. In this paper, we propose a spectrum-hole prediction based channel allocation scheme. To predict spectrum hole, statistic properties of primary user's traffic is used. By using the predicted spectrum hole, channel can be selected opportunistically and it can reduce the possibility of interference with the primary user and increase the efficiency of spectrum utilization. The performance of proposed channel allocation scheme is evaluated by the computer simulation.

In this paper, we proposed a new multi-relay selection and power allocation scheme to maximize network lifetime. To maximize network lifetime, it is important to select appropriate relay node for cooperative communication and allocate power fairly among nodes in a network as well as to minimize total transmitted power. In the proposed scheme, the channel condition and residual power information were considered in multi-relay selection and the allocated power is proportional to the residual power, satisfies the required SNR at destination node and minimizes the total transmission power. In this paper, proposed scheme is base on ldquoamplify and forwardrdquo (AF) model. We evaluate the proposed scheme using extensive simulation and simulation results show that proposed scheme obtains much longer network lifetime than the traditional scheme.

The quality of wireless communication links that employ code-division multiple access (CDMA) mainly suffers from user capacity limit caused by multiple access interference (MAI). To reduce the MAI, we propose parallel interference cancellation assisted channel estimation (PICACE) especially for the indoor reverse link and present theoretical results. We use the signal processing worksystem (SPW) simulator for evaluating 2-D linear 1st order Gaussian interpolation. Because each user's signal on the reverse link may experience different channel fading, we propose reference aided data structure to distinguish each user's own signal. The theoretical results illustrate that PICACE can extend the user capacity of CDMA.

In this paper, the performance of a wideband CDMA single-user return link with the diversity reception is investigated by simulation under a realistic LEO (low earth orbit) mobile satellite channel model. Since there are fundamental differences in the channel characteristics between the LEO mobile satellite and terrestrial mobile systems, such as relatively small delay spread and the varying elevation angles, these factors are taken into account for the channel model. Based on this simulation result, we evaluate the total channel capacity for the multi-beam system with the various system parameters, such as the power efficiency of satellite transponder, encoding scheme and EIRP or G/T of antenna, taken into account. It is shown that the different types of diversity techniques can be successfully applied to combat the performance degradation due to the low elevation angle and thus, warrant the high-quality and low-cost implementation.

The multi-carrier CDMA technique is attractive in a wireless communication system. It can support a high rate data transmission with a high spectral efficiency. The MC-CDMA (multi-carrier code division multiple access) receiver which employs a multiple access interference (MAI) canceller is proposed and analyzed. The receiver first demodulates the received signal to produce the initial data and the channel estimates. Based on these channel estimations, the cancellation scheme essentially creates the replicas of the MAI and removes them for the second improved data decision. Using theoretical analysis and simulation, the performance of MC-CDMA with parallel interference cancellation (PIC) is investigated according to the mean square error (MSE) of the channel estimation. The result shows the considerably large improvement in performance, which is attained by the interference cancellation technique. But if channel estimation is not performed accurately, then the effect of interference cancellation may be significantly decreased.